142 GEORGE C. MATS ON 



the main gorge. One of these postglacial gorges is shown on 

 Map II. 



Map II comprises an area i,ooo yards long, and from 250 to 

 600 yards wide. The lowest part of the map is at the city reser- 

 voir, 880 feet A. T. The contours were mapped on either side 

 of the stream up to 1,000 feet A. T. Above the 1,000-feet con- 

 tour the surface rises very gently to the divides between Ten 

 Mile Creek and the neighboring streams. There are three ridges 

 on the map which extend nearly east and west, and rise to a 

 height of 100 feet above the stream. Each ridge is composed 

 partly of drift and partly of rock covered with drift. 



Oiajinels of Map II. — The stream enters the map through a 

 broad drift floored channel, and, after crossing the rock in the 

 southern ridge through a narrow postglacial gorge, it enters 

 another drift-floored channel, through which it flows to the city 

 reservoir. Below the reservoir the stream flows through the 

 narrow postglacial gorge described earlier in this paper. In 

 addition to the channels now occupied by the stream, there are 

 four other channels within the area of Map II. Two of these 

 channels pass beneath the southern ridge, one east of the present 

 stream (see map. A) , and one west of the present stream, and 

 just south of the house (see map, Z?). There is a channel 

 beneath the middle ridge west of the rock outcrop (see map, ^), 

 and one beneath the northern ridge, east of the rock outcrop 

 (see map, (T). 



Evidence of the existence of chamieh. — The general evidence of 

 the existence of these channels is of two kinds: (i) the trend 

 of the rock outcrops; (2) the existence of well-defined indenta- 

 tions on the upstream side of each of the ridges. These inden- 

 tations were produced by the stream swinging against the soft 

 drift ridges. The drift was not entirely removed from the chan- 

 nel, because the rock in the ridges prevented the formation of a 

 broad meander within these channels. In the case of the 

 channel (-0), west of the postglacial gorge, the drift ridge has 

 been so badly eroded that the rock-walls show above it, and near 

 the southern end of this channel the wall has been exposed down 

 to the bottom of the channel (Plate V). The hypothesis of a 



